1. Field of the Invention
This invention relates to a multilayer anti-reflection film for the ultraviolet range (200-400m.mu.).
2. Description of the Prior Art
Unlike the well-known anti-reflection films intended for the visible range, the corresponding films for the ultraviolet range (200-400m.mu.) have received little attention because of various limitations such as the limited availability of suubstances which are physico-chemically stable and transparent in the ultraviolet range, the manufacturing problem of controlling the thickness of the film, and the wider wavelength range of the ultraviolet range than the wavelength range of the visible range. The only known anti-reflection film for ultra-violet rays is that proposed by O. A. Motovilov (see FIG. 1 of the accompanying drawings). This film, however, cannot be expected to achieve the effect as an anti-reflection film for the full range of 200- 400 m.mu., since it basically employs a two-layer film of 2H.L. which is known as an anti-reflection film for the visible range, whereby the substances such as ZrO.sub.2, HfO.sub.2, Sc.sub.2 O.sub.3, etc. used as substances of high refractive indices cause absorption to occur at the shorter wavelength side (below 260m.mu.). At the same time, the absorption effect cannot be neglected in case of an optical system utilizing a plurality of reflection and refraction surfaces.